A carbon-based material has been widely used as an anode active material of a typical secondary battery. However, development of new materials has been actively conducted due to the growth of the secondary battery market and the demand on power sources for various applications.
Since high output rather than high energy is required for a typical hybrid electric vehicle, amorphous carbon has been mainly used. However, since the current demand for plug-in hybrid electric vehicles or battery electric vehicles has been increased, the demand for a material having high energy density as well as high power characteristics has been rapidly increased.
Accordingly, oxides of transition metal, MOx (where M=cobalt (Co), iron (Fe), nickel (Ni), copper (Cu), or manganese (Mn)), have received attention as an anode active material having very large capacity.
In particular, development of lithium manganese phosphate (LiMnO4) on the basis of Mn as a lithium transition metal oxide has been actively conducted. With respect to Mn, since Mn may be synthesized in air while the price of a raw material is low, it may be considered as a composition that may satisfy both raw material costs and processing costs.
Since LiMnPO4 has a higher density than a graphite-based material while a theoretical capacity of LiMnPO4 (342 mAh/g) is comparable to that of the graphite-based material (372 mAh/g), LiMnPO4 may have a higher energy density per volume.
However, LiMnPO4 has limitations in that its initial efficiency is low and simultaneously, since Mn has low activity, Mn may not easily react with lithium. In the case that charge and discharge are performed by using an electrode formed of LiMnPO4, capacity may not be fully manifested in a typical operating environment and the reaction may proceed only in the case in which charge and discharge are performed at very low current.
In particular, since a reaction voltage of LiMnPO4 with respect to lithium may be high, a voltage of a battery may be low. Also, since there are limitations in the long-term life of the battery due to volume changes during charge and discharge and the reaction with lithium is slow, the output of the battery may be low.